My 8TraXX or MP3AM responds slowly to serial or parallel play commands.
The 8TraXX and MP3 Audio Machine wait for an MP3 sequence header comes along in the currently playing file before transitioning to the next file. If your sequence headers are spaced too far apart, there can be a long delay between command reception and playback
Try re-encoding the files using a different encoder to decrease the size of the data packets in your MP3 data files.